Native look & feel - terminates abruptly on Ubuntu

Hi,

Using the SoapUI 4.5 release on Ubuntu 11.10, if I check the 'Native look & feel' UI setting and restart, SoapUI freezes for a few seconds when the main window opens, then terminates itself. Leaving this setting unchecked gives no problem. Running from the command line, I get:

[rich@rich-laptop:~/Apps/soapui/bin]$ ./soapui.sh 
================================
=
= SOAPUI_HOME = /home/rich/Apps/soapui
=
================================
Configuring log4j from [/home/rich/Apps/soapui/bin/soapui-log4j.xml]
13:46:15,045 INFO  [DefaultSoapUICore] initialized soapui-settings from [/home/rich/soapui-settings.xml]
13:46:17,050 INFO  [WorkspaceImpl] Loading workspace from [/home/rich/default-soapui-workspace.xml]
13:46:17,460 INFO  [WsdlProject] Loaded project from [file:/home/rich/Documents/StockNet-soapui-project.xml]
13:46:18,988 INFO  [SoapUI] Used java version: 1.6.0_26
[xcb] Unknown request in queue while dequeuing
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
java: ../../src/xcb_io.c:178: dequeue_pending_request: Assertion `!xcb_xlib_unknown_req_in_deq' failed.
Aborted

I couldn't see a way of getting any more detailed logs out - if there's any more information required, please shout :-)

Thanks,

Rich.